A known valve opening and closing timing control apparatus which specifies a relative rotation phase between a driving-side rotational member and a driven-side rotational member by a drive force of an electric actuator is disclosed, for example, in JP2008-038886A which is hereinafter referred to as Reference 1. Specifically, Reference 1 discloses a differential type reduction gear mechanism including a ring gear (an inner gear portion) arranged coaxially with a rotation axis, an inner gear (a planetary gear or a second gear member) arranged coaxially with an eccentric axis which is disposed in parallel to the rotation axis, and a drive shaft (a planetary career) internally fitted to the inner gear so that an external teeth portion of the inner gear is meshed with a part of an internal teeth portion of the ring gear.
The valve opening and closing timing control apparatus disclosed in Reference 1 further includes a biasing member (a spring member) at a position not matching or overlapping a position at which the external teeth portion of the inner gear is meshed with the internal teeth portion of the ring gear (i.e., not matching or overlapping an eccentric direction) in an outer periphery of the drive shaft. The biasing member applies a biasing force for meshing the external teeth portion of the inner gear with the internal teeth portion of the ring gear.
Further, in the valve opening and closing timing control apparatus disclosed in Reference 1, a recess portion (an accommodation portion) is provided at the outer periphery of the drive shaft so that a leaf spring constituting the spring member is fitted in the recess portion for exercising the biasing force.
According to the valve opening and closing timing control apparatus disclosed in Reference 1, the inner gear (the planetary gear or the second gear member) is supported at least at three portions including a portion at which an inner peripheral surface of a center bore of the inner gear and an elastic force application line intersect with each other, a portion at which the inner peripheral surface of the center bore of the inner gear and an outer peripheral surface of the drive shaft (the planetary career) make contact with each other, and a portion at which the inner gear and the ring gear (the inner gear portion) are meshed with each other.
With the aforementioned construction, even in a case where a cam fluctuation torque is transmitted to the valve opening and closing timing control apparatus, looseness of the inner gear is restrained so that generation of abnormal noise is inhibited. That is, according to the valve opening and closing timing control apparatus disclosed in Reference 1, the inner gear is supported at the three portions to stabilize the position or posture of the inner gear while a clearance at a meshed portion between the inner gear and the ring gear is also reduced to thereby restrain generation of abnormal noise and phase fluctuation.
At this time, in an assumed construction where the inner gear is arranged to be rotatable about the eccentric axis, the teeth portion of the inner gear and the teeth portion of the ring gear being meshed with each other in a state where a biasing force is applied in a direction where the teeth portions of the inner gear and the outer gear are meshed with each other, the aforementioned meshing state is maintained by the large biasing force. As a result, generation of abnormal noise is restrained and the phase fluctuation is also restrained.
Nevertheless, with the large biasing force, tooth surfaces of the inner gear and tooth surfaces of the ring gear make strong contact with each other to generate sliding resistance that may cause increase of rotation load. As a result, a response speed of the valve opening and closing timing control apparatus may be lowered.
A need thus exists for a valve opening and closing timing control apparatus which is not susceptible to the drawback mentioned above.